In ac,the current magnitude and direction is constantly changing.

The current(magnitude and direction) can be represented by means of a graph.

The top quadrant represents current in one direction and the bottom quadrant represents current in the other direction.

The I_{max} represents the highest value the current would reach (the blue line).

Since the current magnitude is always changing,
it is necessary to identify an average current, or a dc equivalent.

This avearge value is called the average current or I_{rms} (the green line). This is called root mean square, which is really a
complicated way of saying "average".
How do the numbers work?

Easy!
Assume that I_{max} = 20A.

(This would be the peak on the graph)

Calculate the average, I_{rms}.

**Equation**

20 = 1,41(I_{rms})

I_{rms} = 14,18A

You must learn the above equation.